Document laboratory of the Bavarian LKA (Pictures: GDeußing)

When appearances are deceptive

Tough times for crooks

Honesty is the best policy, as the saying goes. Not everyone agrees with this, however. Some people try to push their luck by cheating on a minor or major scale. When they are making checks, the police regularly come across forged documents, such as identity cards sealed in plastic and driving licences or cheques, while crooks are perfectly happy to make illegal changes to wills too. What many of you do not know or suspect: modern science has ways and means of proving that documents have been forged. It is often the case that tiny amounts of ballpoint pen ink, polymer or lacquer particles are already enough to detect forgeries.


When the police are unable to distinguish between "authentic" or "forged" directly at the crime scene, suspicious documents are subjected to a critical inspection in the document laboratory.

After a company went bankrupt, the owner presented a transfer document to the liquidator. This document was dated five years before the bankruptcy and was supposed to prove that the owner had already transferred his share portfolio (worth millions), his premium cars and his valuable collection of firearms to his wife a considerable time ago. The consequence of this would have been that the creditor banks would have had no access to this property and would have gone empty-handed - if they had not suspected fraud and reported the case to the police. On the assumption that the man had not concluded the transfer contract until after the bankruptcy and had simply backdated it, the police were commissioned to check the date when the document was produced.


The initial emphasis there is on comparison with samples from the collection as well as with forgeries that have been kept as evidence and are marked with a red dot.

Forged documents are not always obvious. "This is because things are the way they are", says Dr Jürgen Bügler, a chemist at the forensics institute run by the Bavarian criminal investigation authorities (LKA) in Munich. After all, it is not possible for any policeman to know all the official documents in circulation at the national and international level, let alone to distinguish between genuine and forged ones. "And no-one has to either", emphasises Jürgen Bügler. Reasonable suspicion is all that is needed to attract the attention of the detectives: suspicious behaviour by the person in question, a small manipulation of the document, perhaps a photo that is missing in a driving licence. The scientists at the forensics laboratory take it from there.


The most important resources needed here is a so called linen tester, a small magnifying glass that magnifies up to ten times, .

The legal situation is clear

"Anyone who produces a bogus document, forges a genuine document or uses a bogus or forged document for deceptive purposes in legal transactions shall be sentenced to up to five years in prison or the payment of a fine". § 267 of the German Criminal Code (StGB) states that it is an offence even to attempt to do these things. The Bavarian criminal investigation authorities in Munich rely on the know-how and experience of their engineers and scientists as well as on proven analytical techniques to solve cases of document forgery. A look at the document laboratory operated by the Bavarian criminal investigation authorities reveals that thermal desorption GC/MS is one of the central tools used to inspect dubious documents.


The scientific investigation starts with an inspection and a comparison between the "corpus delicti" and, if there is one, an original from the LKA files.

The scientific investigation starts with an inspection and a comparison between the "corpus delicti" and, if there is one, an original from the LKA files. "A linen tester, which is a magnifying glass that magnifies up to ten times, is the most important tool during this phase; it is used to check the obvious safety features, like the watermark, fine line structures - known as "guilloches" - or special colour gradients", explains Dr Jürgen Bügler. If the preliminary visual inspection with a magnifying glass does not produce any significant evidence, investigation of the dubious document is continued under a microscope.


Manipulations using a razor or entries that have been eliminated in other ways can be made visible by examining luminescence.

Dr Bügler: "Manipulations using a razor or other entries in the document that have been eliminated manually can be detected by checking luminescence and/or measuring remission." In many cases, it is possible to work out the order in which entries were made too: "If someone has added something to a copied or printed document subsequently using a ballpoint pen or has subsequently inserted text passages in a signed document using a printer or photocopying machine, this can under certain circumstances be proved on the basis of differences in luminescence", the expert points out.


The order in which entries have been made can be investigated here too. Below: the black line is toner (photocopying machine), while the orange line is a luminescence image of the writing medium.

What happens, on the other hand, if what is involved is not an official government document like an identity card sealed in plastic or a passport but, let us say, a personal cheque instead, with which the recipient was, surprisingly, able to withdraw more money than the issuer of the cheque had planned? What if a will suddenly favours someone to whom the deceased had been unwilling to give even a cent while still alive? What most crooks do not know: no matter how unobtrusively a document is manipulated, there are still clear signs that manipulation has taken place! Dr Jürgen Bügler: "Once we have received the dubious document, the chances are good that potential forgery will be detected conclusively."


The chemist gives an obviously fraudulent cheque that was reported to the police as an example. The amount entered on the bank document by the issuer was increased many times over by adding a number of zeroes at the end without his permission, according to the issuer. The latter therefore took legal action and the case was investigated by Dr Jürgen Bügler, who the court appointed as an independent expert. So that you know right away how the story ended: the attempted fraud was confirmed, the person behind it was convicted and went to prison. What procedure did the LKA scientists adopt, however?


The orange luminescence of the writing medium is on top of the toner, i.e. it was applied later.

Analysis of the writing medium used, i.e. the ink or the toner with which the document was manipulated, is the key to proving that something has been forged. Dr Jürgen Bügler: "Precise analysis of the writing medium used plays a crucial role in determining the authenticity of a document and/or the age of an entry." The order in which the entries have been made in the dubious document can also be ascertained.


The composition of the colorants they contain essentially distinguishes the various writing media and can be determined comparatively simple, quickly and reliably using thin-layer chromatography, with convenient filing afterwards.

Back to the criminal investigation authorities. The forensic department of the Bavarian LKA has been collecting media like ballpoint pen ink since 1952. The collection consists of 6,000 samples and is updated and extended on an ongoing basis. "The composition of the colorants they contain essentially distinguishes the various writing media and can be determined comparatively simple, quickly and reliably using thin-layer chromatography, with convenient filing afterwards," explains Dr Jürgen Bügler. A comparison of the chromatograms produced enables the writing medium used to be identified and to be distinguished from other writing media - the latter being one of the keys to solving document forgery cases. In order to determine the time when a handwritten or printed entry was made, the expert analyses the solvent used in the writing medium, which evaporates in the course of time. Dr Bügler's conclusion: "It is possible to ascertain the age of documents in this way."


Apart from the Bavarian criminal investigation authorities, only the document laboratory of the Secret Service in the United States of America has a similarly large collection of writing media.

Back to the personal cheque: in order to find out which writing medium/media was/were used, a piece of paper with writing on it is removed from the dubious section of the cheque - where the zeroes were written in our example - and is investigated in greater detail. The aim in doing this, Dr Bügler explains, is to extract and determine the volatile compounds in the writing medium, e.g. the ballpoint pen ink. He stresses that this is not as simple as it might sound.

Because the work is made more difficult by the small quantity of analytes and the unstable paper matrix, which - it is reported - absorbs the interesting chemical compounds in the long run and reduces the amount of them available for detection purposes. It should not be forgotten in this context that the sample quantities are extremely small anyway. To make it clear what we are talking about here: according to Dr Jürgen Bügler, a line about one centimetre long that is drawn using a ballpoint pen requires about ten nanograms (ng) of ink, six ng of which are solvent, some 95 per cent of which have already evaporated within the first day; the substrate for the ink is about 100µg of paper. The scientist comments: "It is our job to determine the residual solvent - not something that you can do on the side".

The lack of a benchmark that can be used as a reference proves to be an additional challenge to the scientist. "A line on paper can be very inhomogeneous", says Dr Jürgen Bügler. So you can never say exactly how much ballpoint pen ink has actually been applied to the paper. Classic quantitative analysis that is used in forensic science, e.g. to determine drug residue, is not therefore a viable option when trying to detect document forgeries.


Ageing, which happens at speeds that differ from writing medium to writing medium, is also said to play a major role: colorants fade, solvents evaporate or are adsorbed by the paper matrix. Resins (bonding agents) crosslink and cure. Dr Bügler: "Many different processes occur that need to be taken into consideration in evaluation of the analytical results obtained". The expert stresses that the method and sample preparation procedure therefore have to satisfy the most exacting of requirements.


If a comparison of the thin-layer chromatograms does not provide any information about composition or entries in a document need to be tested to determine their composition or age, the automated GERSTEL TDS GC/MS with online derivatisation is the process of choice.

The most important tool in the solution of document forgery cases is gas chromatography in connection with mass selective detection (GC/MS). "Liquid extraction is used to extract the ink", reports Dr Jürgen Bügler, even though this is a relatively difficult undertaking, because the amount of the substance and the contents of the analyte are very small, as indicated above. An alternative is pyrolysis combined with gas chromatography (GC) for separation purposes and mass selective detection (MS) to determine the pyrolysis products, i.e. thermal decomposition of the sample material at about 400°C without oxygen. (For further details see Pyrolysis GC/MS.)

This procedure is apparently in widespread use, but tests have shown that "the paper disintegrates and the pyrolysis products make it more difficult to determine the components of the ink". In order to be able to determine the interesting analytes smoothly, Dr Bügler had the idea of reducing the temperature: "This approach led us to thermal desorption". The scientist reveals that this is an effective way to extract the volatile analytes in a simple, efficient and temperature-programmed way, to enrich them in a cold trap and to make the analysis more sensitive as a result. This is said to be completely impossible with conventional pyrolysis equipment. In order to be able to detect and measure substances that disintegrate easily or do not evaporate readily via gas chromatography, they frequently need to be changed chemically (derivatised). A laborious and demanding process for which the forensic experts in Munich have, however, found a solution that has given them an international reputation in the document forgery investigation field.

Not only the Bavarian criminal investigation authorities (LKA) but also the canton police in Zurich and other forensic laboratories all over the world are in the meantime using the Bavarian LKA's method to detect document forgeries. Not surprisingly, as Dr Jürgen Bügler explains: "The volatile contents of writing media can be investigated efficiently, sensitively and reliably with this system without destroying the paper matrix in the process."

Minute scraps with dimensions of 5 mm x 1 mm are enough to solve complicated criminal cases that it has not been possible to settle before. Going back to our example: "The attempt to obtain more money than the issuer had planned by manipulating a personal cheque was only successful for a short time", reports Dr Bügler. After he had investigated the ballpoint pens used, he was in the final analysis able to prove the document forgery conclusively, thus enabling the victim to get back what was rightfully his. The results were similar with the transfer contract too. The analysis allowed it to be concluded with almost absolute certainty that the businessman who went bankrupt only concluded the contract with his wife after he went bankrupt and not at the time he claimed five years before", explains Dr Jürgen Bügler. Sophocles (496-406 BC) understood a long time ago: ""Rather fail with honour that succeed by fraud."